NIDDK and the American Diabetes Association have recommended routine screening for "pre-diabetes" - a major public health problem - but we do not know how best to detect it. The U.S. is experiencing a dramatic rise in both type 2 diabetes and its antecedent, "pre-diabetes" (mostly impaired glucose tolerance, IGT). Diabetes Prevention Program results show that progression from IGT to diabetes can be decreased, but patients can only be directed to risk reduction programs if they are recognized; detecting IGT will be especially important for minority populations such as African-Americans, who suffer disproportionately from diabetes. However, since we don't screen for IGT, many IGT patients progress to diabetes, and already have complications and increased cardiovascular risk when they are finally diagnosed. Risk factor-based "predictive models" might identify individuals who should have an OGTT to detect IGT, but such approaches may have limited applicability, and are generally not used to screen for gestational diabetes, where the metabolic defect is similar to IGT. Hypotheses: Two-step screening by a one hour oral glucose challenge test (GCT) followed, if abnormal, by an OGTT will have good predictive ability to identify IGT, and will be superior to "predictive models" in both diagnostic efficiency and cost-effectiveness. Specific Aims: (1) To validate the GCT as a reliable predictor of IGT, we will perform both the GCT and an OGTT in a large number of African-Americans and Caucasians, with two objectives: (a) to identify cutoff levels which provide optimal test characteristics in both groups despite variation in prandial status or time of day; (b) to determine how predictive ability is modified by the presence of potential risk factors (age, ethnicity, family history, BMI, waist-hip ratio, dyslipidemia, hypertension, etc.); (2) To compare GCT screening to "predictive model" screening, we will evaluate both predictive ability and cost-effectiveness. Fulfilling the potential of the DPP demands a highly generalizable, low-cost screening strategy; our multidisciplinary team will translate approaches proven beneficial for gestational diabetes into a cost-effective method to identify individuals who could benefit from programs to decrease progression from IGT to diabetes, and reduce cardiovascular risk. Starting management soon enough is a major problem in diabetes care - particularly for minorities which suffer disparities in health. By applying existing knowledge to disease control and prevention, our Specific Aims are the critical first steps to solve this problem.